Skip to main content

shadowing-import

shadowing-import Function

Syntax:

shadowing-import symbols &optional package → t

Arguments and Values:

symbols—a designator for a list of symbols.

package —a package designator . The default is the current package.

Description:

shadowing-import is like import, but it does not signal an error even if the importation of a symbol would shadow some symbol already accessible in package.

shadowing-import inserts each of symbols into package as an internal symbol, regardless of whether another symbol of the same name is shadowed by this action. If a different symbol of the same name is already present in package, that symbol is first uninterned from package. The new symbol is added to package’s shadowing-symbols list.

shadowing-import does name-conflict checking to the extent that it checks whether a distinct existing symbol with the same name is accessible; if so, it is shadowed by the new symbol, which implies that it must be uninterned if it was present in package.

Examples:

(in-package "COMMON-LISP-USER") → #<PACKAGE "COMMON-LISP-USER"> 
(setq sym (intern "CONFLICT")) → CONFLICT 
(intern "CONFLICT" (make-package ’temp)) → TEMP::CONFLICT, NIL 
(package-shadowing-symbols ’temp) → NIL 
(shadowing-import sym ’temp) → T 
(package-shadowing-symbols ’temp) → (CONFLICT)

Side Effects:

shadowing-import changes the state of the package system in such a way that the consistency rules do not hold across the change.

package’s shadowing-symbols list is modified.

Affected By:

Current state of the package system.

See Also:

import, unintern, package-shadowing-symbols

Expanded Reference: shadowing-import​

Basic Usage: Importing a Symbol and Adding It to the Shadowing List​

shadowing-import is like import, but it does not signal a name conflict error. The imported symbol is added to the package's shadowing symbols list.

(defpackage "ORIGIN-SI" (:use) (:export "ITEM"))
(make-package "DEST-SI" :use '())
(intern "ITEM" "DEST-SI")  ; a different symbol with the same name

(find-symbol "ITEM" "DEST-SI")
;; => DEST-SI::ITEM
;; => :INTERNAL

;; shadowing-import replaces DEST-SI::ITEM with ORIGIN-SI:ITEM
(shadowing-import (find-symbol "ITEM" "ORIGIN-SI") "DEST-SI")
;; => T

(find-symbol "ITEM" "DEST-SI")
;; => ORIGIN-SI:ITEM
;; => :INTERNAL

(package-shadowing-symbols "DEST-SI")
;; => (ORIGIN-SI:ITEM)

Resolving Name Conflicts Between Used Packages​

shadowing-import is useful for resolving conflicts when two used packages export symbols with the same name.

(defpackage "A-SI" (:use) (:export "CLASH"))
(defpackage "B-SI" (:use) (:export "CLASH"))
(make-package "C-SI" :use '())

;; Import A's CLASH as the shadowing symbol before using both packages
(shadowing-import (find-symbol "CLASH" "A-SI") "C-SI")
(use-package '("A-SI" "B-SI") "C-SI")
=> T

(find-symbol "CLASH" "C-SI")
;; => A-SI:CLASH
;; => :INTERNAL

Difference from import​

Regular import would signal an error if a different symbol with the same name is already accessible. shadowing-import silently replaces it.

(defpackage "NEW-SI" (:use))
(intern "THING" "NEW-SI")

;; Create an unrelated symbol to import
(defpackage "OTHER-SI" (:use) (:export "THING"))

;; import would signal an error here, but shadowing-import does not
(shadowing-import (find-symbol "THING" "OTHER-SI") "NEW-SI")
=> T

;; The old THING is gone, replaced by OTHER-SI's THING
(find-symbol "THING" "NEW-SI")
;; => OTHER-SI:THING
;; => :INTERNAL

The Symbol is Added to package-shadowing-symbols​

(make-package "SHADOW-LIST-SI" :use '())
(package-shadowing-symbols "SHADOW-LIST-SI")
=> ()

(shadowing-import 'cl:car "SHADOW-LIST-SI")
=> T

(package-shadowing-symbols "SHADOW-LIST-SI")
=> (CAR)